Patent GB-678052-A (GB)
Title: Improvements in and relating to dynamo-electric machines
IPC: H02K27/12
Filed: 1950-05-08
Abstract: 678,052. A.C. commutator motors. BRITISH THOMSON - HOUSTON CO., Ltd., and MAGGS, A. H. March 19, 1951 [May 8, 1950], No. 11384/50. Class 35. A stator-fed A.C. commutator motor which gives the same output at the same speed when used on supplies of various frequencies but the same voltage, has a tapped stator winding and the tapped portions are used alternatively or simultaneously as part of the primary winding, and as the winding providing a voltage which is injected into the rotor winding to raise or lower the motor speed. As shown in Figs. 1 and 2 for a two-pole threephase motor, the commutated rotor winding 1 is engaged by brushes 2, 3, 4, while the stator windings are tapped at 12, 15, 18 so that the phase windings are divided into parts 5 and 6, 7 and 8, 9 and 10, respectively, the outer terminals 11, 14, 17 being connected to the supply. In Fig. 1, the brushes are shorted together and the inner terminals 13, 16, 19 of the stator phases are joined to form a star-point, this connection producing a speed of 3000 r.p.m. at 50 cycles. In Fig. 2, the brushes are connected to the inner points of the stator windings while the tapping points are connected together to form the star-point. By this arrangement the voltage in the tapped portions bucks that in the rotor winding so that the motor speed is reduced below the normal near-synchronous speed and may be 3000 r.p.m. on a 60-cycle supply, without change in the working flux of the machine. In another connection, the inner points of the stator windings are joined to form the star-point while the brushes are connected to the tapping-points. By this connection the voltage in the tapped portion boosts that in the rotor and the motor speed is raised, e.g. to 3600 r.p.m. on 50 cycles. Finally, the brushes may be shorted together and the tapping points connected to form the star-point leaving the tapped parts of the windings unconnected so that no additional voltage is injected at the brushes and the motor runs at 3600 r.p.m. on a 60-cycle supply, again without the flux being altered. In a modified form, Fig. 5, in which no star-point connection is used, additional brushes 20, 21, 22 are used, so that each phase has two diametrically-opposed brushes, the rotor providing a virtual neutral point. In the connection shown in Fig. 5, which produces a speed of 3000 r.p.m. at 50 cycles, both the main brushes 2, 3, 4 and the additional brushes 20, 2], 22 of each phase are connected to the inner terminals of the stator phase windings. In a modified connection, producing the same speed at 60 cycles, the additional brushes are connected to the tapping- points, while if the additional brushes are left connected to the inner points and the main brushes are connected to the tapping points, the machine runs at 3600 r.p.m. on a 50-cycle supply. Finally, if both main and additional brushes are connected to the tapping points a speed of 3000 r.p.m. is produced on a 60-cycle supply. The three-phase machines shown may be fed with a single-phase across two of the phases and a phase-splitting condenser may be used in the remaining phase.